The label is the law. Read your product's label before you mix or apply; the rates here come from the labels listed under Sources.
- Active ingredient
- S-methoprene (CAS 65733-16-6)
- Chemical class
- Insect growth regulator (juvenile hormone mimic).[1][3]
- Mode of action
- IRAC Group 7A: Juvenile hormone mimics: juvenile hormone analogues[3]
- Signal word
- Precor IGR Concentrate (Zoecon RF-291 Emulsifiable Concentrate): Caution[2]
How it works
By mimicking an insect hormone, methoprene disrupts molting, egg-laying, egg-hatching and the change from immature stage to adult, so insects cannot reproduce.[1]
On the Precor label, flea eggs laid on treated surfaces and larvae crawling onto them never develop into adults.[2]
In the environment
Sunlight and microbes break methoprene down quickly: in soil half is gone in 10 to 14 days, and in water in 1 to 28 days depending on sunlight.[1]
Where it is used
The label says it prevents adult flea emergence for up to 7 months on carpets, upholstered furniture and pet sleeping areas, treating 1,500 sq ft per gallon of spray.[2]
It does not affect adult fleas or flea pupae, so when many biting adults are present the label says to tank-mix it with an adult-flea insecticide.[2]
Methoprene is often added to other insecticides because it acts on insects that survive the other ingredient.[1]
Products and registrations
| Product | Registrant | EPA Reg. No. | Active % | Formulation | Signal word |
|---|---|---|---|---|---|
| Precor IGR Concentrate (Zoecon RF-291 Emulsifiable Concentrate)[2] | Wellmark International (Zoecon) | 2724-352 | 1.2% | emulsifiable concentrate | Caution |
Label rates
| Product | Use | Pests | Rate |
|---|---|---|---|
| Precor IGR Concentrate (Zoecon RF-291 Emulsifiable Concentrate) | Indoors: carpets, upholstered furniture, throw rugs and pet bedding | Flea eggs and larvae (prevents adult emergence) | 1 fl oz per gal of water[2] Makes about a 0.007% S-methoprene spray. Apply 1 gallon of the mix per 1,500 sq ft with a low-pressure fan-tip sprayer, including under cushions. Test upholstery for staining first. |
How to apply it, step by step
1. Protective gear
- The label lists no protective gear: it is harmful if absorbed through the skin and causes moderate eye irritation, so keep it off your skin and out of your eyes, and wash with soap and water after handling.[2]
2. Before you spray
- It stops flea eggs and larvae from becoming adults; it doesn't kill adult fleas or pupae already present. With many biting adults around, the label says to tank-mix it with an EPA-registered adult flea killer.[2]
- Treat your pets with an effective EPA-registered flea product too, so they don't keep bringing adult fleas inside; ideally apply it before flea season.[2]
- It is combustible: keep it away from heat and open flame. On upholstery, test a hidden spot first; it generally doesn't stain anything water alone wouldn't.[2]
3. Mixing
- Put ½ gallon of water in the sprayer, add 1 fl oz of concentrate, shake, then add the other ½ gallon and shake again (about 0.007% methoprene). Shake before each use.[2]
- If you tank-mix with an adult flea killer, add that product first, agitate, then add this one, fill the tank and agitate again.[2]
4. Applying
- Spray 1 gallon of the mix per 1,500 sq ft with a low-pressure sprayer and a fan tip.[2]
- Treat everywhere fleas live: carpets, throw rugs, upholstered furniture (including under the cushions), and pet sleeping and bedding areas.[2]
5. After you spray
- Stay off treated surfaces until they're dry.[2]
- It prevents adult fleas from emerging for up to 7 months (210 days).[2]
First aid
- In the eyes, rinse slowly and gently for 15 to 20 minutes, removing contact lenses after the first 5 minutes; on skin or clothing, take off contaminated clothing and rinse for 15 to 20 minutes; call a poison control center or doctor.[2]
- It contains petroleum distillates: if swallowed, call a poison control center or doctor right away, don't induce vomiting unless told to, and don't give the person any liquid.[2]
Storage, spills and disposal
- Store it in a cool place away from heat or open flame.[2]
- Don't reuse the empty container: rinse it three times (about ¼ full of water, shaken 10 seconds, rinse water added to the sprayer), then recycle it if you can or put it in the trash.[2]
From the safety data sheet
- The concentrate is a very light straw-colored, transparent liquid, and the SDS uses the signal word Danger: it may be fatal if swallowed and it enters the airways, causes skin and eye irritation, and may cause drowsiness or dizziness.[4]
- It contains petroleum distillate, so if someone swallows it, call a poison control center or doctor right away and don't induce vomiting.[4]
- On skin, wash with plenty of soap and water and get medical advice if irritation develops; in the eyes, rinse cautiously with water for several minutes, removing contact lenses if that is easy, and keep rinsing.[4]
- It is a combustible liquid: keep it away from flames and hot surfaces, don't walk through a spill, and soak up small spills with sand or another non-combustible absorbent.[4]
- Store it locked up in a cool, well-ventilated place, and keep large spills out of waterways, sewers and basements.[4]
Safety and environmental hazards
People
The label signal word is CAUTION: harmful if absorbed through the skin and causes moderate eye irritation; it contains petroleum distillates and is combustible. Methoprene can mildly irritate the eyes, lungs or skin, is rapidly broken down and excreted, and is not expected to contribute to cancer based on long-term animal studies.[2][1]
Pets
Avoid contact with treated surfaces until they are dry. Dogs fed extremely high doses (10 g/kg) vomited and showed behavior and breathing changes, but at half that dose showed no signs; the label says to treat fleas on the pets themselves with a registered pet product.[2][1]
Bees and pollinators
Methoprene appears to be low in toxicity to adult bees, though bee larvae may be more sensitive.[1]
Fish and water
Methoprene is very highly toxic to freshwater invertebrates, moderately toxic to some fish, and can accumulate in fish tissue; this product is for indoor use.[1][2]
Common questions
- Does methoprene kill adult fleas?
- No. It stops eggs and larvae from becoming adults; the label says existing adult fleas and pupae are not affected and recommends adding an adult-flea insecticide when many adults are present.[2]
- How long does Precor last indoors?
- The label says it prevents adult flea emergence for up to 7 months (210 days).[2]
- How much Precor per gallon?
- 1 fluid ounce per gallon of water, applied at 1 gallon per 1,500 square feet.[2]
Sources
- National Pesticide Information Center, “Methoprene General Fact Sheet.” npic.orst.edu/factsheets/methogen.html (accessed 2026-10-06)
- U.S. EPA Pesticide Product Label System, “Zoecon RF-291 Emulsifiable Concentrate with Precor label, EPA Reg. No. 2724-352 (EPA-stamped, Feb. 19, 2021).” www3.epa.gov/pesticides/chem_search/ppls/002724-00352-20210219.pdf (accessed 2026-10-06)
- Insecticide Resistance Action Committee, “IRAC Mode of Action Classification Scheme, Version 11.5 (Feb. 2026).” irac-online.org/documents/moa-classification/ (accessed 2026-10-06)
- Wellmark International (Zoecon), “Zoecon Precor IGR Concentrate Safety Data Sheet (Wellmark International, prepared July 20, 2015, revised December 22, 2015; lists EPA Reg. No. 2724-352 and Zoecon RF-291 Emulsifiable Concentrate, the label on this page; copy hosted on a pest control distributor's label server).” label.westernpest.com/%5Cfiles_techservices%5Clive%5Czoecon.precorIGR122215.sds.pdf (accessed 2026-10-19)